Electrical position-encoders



Feb. 22, 1966 c. J. WAYMAN 3,237,189

ELECTRICAL POSITION-ENCODERS Filed Aug. 28. 1962 4 Sheets-Sheet 1 FITT'DRNEYS.

Feb. 22, 1966 c, J, wAYMAN 3,237,189

ELECTRICAL POSITION-ENCODERS Filed Aug. 28, 1962 4 Sheets-Sheet 2 WWW 3142, hwm;

HTTOR NeYS Feb. 22, 1966 c. J. WAYMAN 3,237,189

ELECTRICAL POSITION-ENCODERS Filed Aug. 28. 1962 4 Sheets-Sheet 5 (261 JOHN U a mi QM q'rTo RNEYS 4 Sheets-Sheet 4.

Detector L N N M R m IW D1 C. J. WAYMAN ELECTRICAL POSITION-ENCODERS Feb. 22, 1966 Filed Aug. 28. 1962 5 C. F f

United States Fatent O 3,237,189 ELECTRICAL POSllTION-ENCQDERS Cecil John Wayman, Stanmore, England, assignor to The General Electric Company Limited, London, England Filed Aug. 28, 1962, Ser. No. 220,013

Claims priority, application Great Britain, Aug. 30, 1961,

31,280/61 13 Claims. (Cl. 340-347) This invention relates to electrical position-encoders.

According to the present invention, in an electrical position-encoder, a first electrical conductor and a plurality of second electrical conductors extend through the spaces between teeth of a ferromagnetic core so that there is a multiplicity of such spaces through which pass both the first conductor and at least one of the second conductors, and a ferromagnetic element is mounted for movement relative to the core with said element adjacent to the free ends of a pair of adjacent teeth of the core, the paricular pair depending upon the position of the element relative to the core, so that the reluctance of the magnetic circuit through the teeth of said pair is less than when said element is not adjacent to the free ends thereof, said teeth lying one after another along a path that is substantially parallel to the path of movement of said element relative to the core, and the arrangement being such that the inductive couplings between the first conductor on the one hand, and the second conductors on the other hand are together characteristic of the position of the ferromagnetic element relative to the core.

Each second conductor may extend through each of said spaces, and may extend through as many of said spaces in the same general direction as the first conductor as it does in the opposite general direction to the first conductor, so that neglecting the effect of the ferromagnetic element, there is substantially zero overall inductive coupling between the first conductor and each second conductor. Each second conductor and the first conductor may extend in the same general direction as one another through N spaces between the teeth of one or more spaced groups of adjacent teeth on the core, N being an integral power of two the value of which is constant for each second conductor and is difi'erent between at least some of the second conductors.

The ferromagnetic core may be an annular core, the ferromagnetic element being, carried by a rotatable shaft that is coaxial with the core. In these circumstances the teeth on the core may be spaced apart from one another around the inner circumference of the core and may extend radially inwards of the core, the ferromagnetic element being carried by the shaft to rotate therewith internally of the teeth.

Two first conductors may be provided, the two first conductors extending alternately with one another through the spaces between consecutive teeth on the core, whereby the inductive couplings between either first conductor on the one hand, and the second conductors on the other hand, are together characteristic of the position of the ferromagnetic element relative to the core. In this case the ferromagnetic element may be such that it at all times lies adjacent to the free ends of the teeth of two consecutive pairs of teeth on the core, the paricular pairs depending upon the position of said element relative to the core.

Alternating electric current may be applied to excite the first conductor, or where two first conductors are provided, to excite both first conductors or only one at a time, the arrangement being such that a corresponding signal that is in-phase or anti-phase with the exciting signal (depending upon the relative position of the ferromagnetic element and the core) is as a result induced in each second conductor. Electric pulses rather than alternating current may be used as the exciting signal, the arrangement being such that pulses that are of one or the other polarity (depending upon said relative position) are in this case induced in each second conductor. With either exciting signal, the signals that appear in the second conductors are in combination characteristic of said relative position. The exciting signal, whether an alternating current signal or a pulse signal, may be applied to the second conductors in turn rather than to the one or more first conductors. In this case a train of signals that is representative of said relative position is induced in the one or more first conductors.

An electrical position-encoder in accordance with the present invention, together with electrical position-encoding arrangements employing such position-encoder, will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a part-sectional side elevation of the position-encoder;

FIGURE 2 is an enlarged section taken on the line II- II of FIGURE 1 (the sectional part of FIGURE 1 being taken on the line 1-1 of FIGURE 2) in which only a portion of the electrical winding arrangement of the position-encoder is shown;

FIGURES 3 and 4 are diagrammatic representations showing the winding arrangement of the position-encoder;

FIGURE 5 shows an electrical arrangement which includes the position-encoder of FIGURES l and 2, and which is for providing output electric signals that are characteristic of the angular position of a shaft within one revolution; and

FIGURE 6 shows an electrical arrangement which includes two position-encoders both as shown in FIGURES l and 2, and which provides output electric signals that are characteristic of the angular position of a shaft Within sixteen revolutions.

Referring to FIGURES 1 to 4, an annular ferro-magnetic core 1 is mounted within a metal casing 2, the core 1, which is laminated, having thirty-two inwardly projecting teeth 3 that are equally spaced from one another about an axis 4 of the core 1. A ferrite element 5 for varying the magnetic reluctance between pairs of adjacent teeth 3, is mounted upon a rotatable shaft 6 that is coaxial with the core 1. The element 5 is carried by the shaft 6 to lie adjacent the free ends of teeth 3, and

' to bridge effectively the thirty-two spaces 7 between the teeth 3 in succession as it rotates with the shaft 6. In the region of the free-ends of the teeth 3 the width of the element 5 is twice the tooth-pitch of the teeth 3, so there is always one of the thirty-two spaces 7 bridged by the element 5. The thirty-two spaces 7 between the teeth 3 are individually identified as spaces 700 to 731. Two first electrical conductors 8 and 9 (referenced 8, 9 in FIGURE 1) are wound round the teeth 3 to lie in the even spaces 700, 702, 704 730, and the odd spaces 701, 703, 705 731, respectively. The directions in which the conductors 8 and 9 are wound alternate between the successive even and odd spaces 7 respectively. Five second electrical conductors 10 to 14 (referenced collectively as 1044 in FIGURE 1) are also wound round the teeth 3 to lie within the spaces 7. The individual conductors 8 to 14, and the manner in which they are wound on the core 1, is shown partly in FIGURE 2 and fully in FIGURES 3 and 4. In FIGURE 2 each conductor 8 to 14 is shown for clarity as passing only once through any space 7, and in FIGURES 3 and 4 each conductor is shown as though wound only once round each tooth 3. The conductors 8 to 14 are in fact wound round each tooth 3 some ten or twenty times.

Referring more particularly to FIGURES 3 and 4, the

two ends of the conductor 8 are connected to a pair of terminals 15 and 16, and the two ends of the conductor 9 are connected to a pair of terminals 17 and 18. The conductors 10 to 14 on the other hand are each connected at one end to a common terminal 19, and at their other ends are connected to terminals 20 to 24 respectively. The connections from the conductors '11 to 14 (FIGURE 4) to the terminal 19 (FIGURE 3) are shown as male via a common lead 26. The ten terminals 15 to 24 (of which only the terminal 13 is indicated in FIGURE 1) are mounted on, but are electrically insulated from, a metal end-plate 25 carried by the casing 2 (see FIG- URE 1).

The conductors 10 to 14 are found on the core 1 to each extend through eight of the sixteen even spaces 7 in the same direction as the conductor 8, and through the other eight even spaces 7 in the opposite direction to the conductor 8. Similarly, each conductor 10 to 14 extends through eight of the sixteen odd spaces 7 in the same direction as the conductor 9, and through the other eight odd spaces 7 in the opposite direction to the conductor 9. (The directions in which the respective conductors 8 to 14 are wound are indicated by arrows in FIGURES 3 and 4, and by crosses and circles in FIGURE 2; in FIGURE 2 the crosses and circles indicate the respective directions into, and out of, the plane of the figure.) If with this winding arrangement the effect of the ferromagnetic element 5 is neglected, the inductive coupling between each conductor 8 and 9 and each conductor 10 to 14 in one sense is equal to the inductive coupling in the other sense, so that there is, overall, zero inductive coupling between each conductor 8 and 9 and each conductor 10 to 14.

The conductors 10, 11 and 12 extend in the same directions as the conductors 8 and 9 through groups of two, four, and eight, adjacent spaces respectively, of the spaces 7, and the conductors 13 and 14 extend in the same directions as the conductors 8 and 9 through different groups of sixteen adjacent spaces 7. For example the conductor 11 extends through the four groups of four spaces 706 to 709, 714 to 717, 722 to 725, and 730 to 701 in the same directions as the conductors 8 and 9, and, consequently, extends in the opposite directions to the conductors 8 and 9 through the four groups of four spaces 702 to 705, 710 to 713, 718 to 721, and 726 to 729.

The winding pattern of each second conductor 10 to 14 is such that its direction is the same as that of the relevant first conductor 8 or 9 through each space 7 of an individual combination of the spaces 7. Thus within each of the spaces 7 there is an individual, unique combination of second conductors that have the same direction as the relevant first conductor or 9 in that space. Additionally, within the same space 7 there is the complementary individual combination of second conductors that are oppositely directed. For example, the space 704 is characterized by a combination of three of the conductors 10 to 14, the conductors 10, .1 3 and 14, that extend through this space in the same direction as the conductor 8 (and likewise, is characterised by the complementary combination comprising the conductors 11 and 12 that extend through the space 704 in the 0pposite direction to the conductor 7). On the other hand the space 705 is characterised by the combination of conductors 13 and 14 that pass through this space in the same direction as the conductor 9 (and likewise, is characterised by the complementary combination comprising the conductors 10, 11 and 12 that pass through the space 705 in the opposite direction to the conductor 9).

The effect of the ferromagnetic element in bridging any one of the spaces 7 is to enhance, within the relevant space, the inductive coupling between whichever of the conductors 8 and 9 lies in that space, and each of the conductors to 14. The senses of the resultant inductive couplings between the individual conductors 10 to 14 and the appropriate conductor 8 or 9, are dependent upon the directions in which the conductors 10 to 14 are wound through the bridged space 7. Thus, the combination of those of the conductors 10 to 14 between which on the one hand, and the relevant conductor 8 or 9 on the other hand, the inductive coupling is of one predetermined sense, is characteristic of the space 7 that is bridged. This combination is also therefore, characteristic of the angular position of the element 5 and the shaft 6, relative to the core 1.

The position-encoder that is described above with reference to FIGURES 1 to 4, may be operated in either of two basic ways in dependence upon whether a digital representation of the angular position of the shaft 6 is required in the parallel or serial mode. When the digital representation is required in the parallel mode then an alternating current signal, or a pulse train, is applied to excite the two conductors 8 and 9, and five output signals are derived from the inudced signals which appear in the five conductors 10 to 14 respectively. On the other hand, when the digital representation is required in the serial mode, pulses are applied in succession to the five conductors 10 to 14, and a series of five output signals is derived from the series of five pulses induced in the conductors 3 and 9.

An example of the manner in which the position-encoder is used to provide a digital representation of shaft position in the parallel mode will now be described with reference to FIGURE 5. In FIGURE 5 the position-encoder described above with reference to FIGURES l to 4 is given the general reference 27.

Refering to FIGURE 5, a source 28 of alternating current having a frequency of twenty-five kilocycles per second, is connected to the terminals 15 and 17 of the apparatus 27 to excite the two conductors 8 and 9 concurrently The terminals 16, 18 and 19 are connected to earth, and the terminals 20 to 24 are connected to apply the signals that are induced in the conductors 10 to 14 to five phase detectors 29 respectively (of which only one is shown). The signal supplied by the alternating current source 28 is also applied to each phase detector 29 as a reference against which to determine whether the signal induced in the relevant conductor 10 to 14 is in-phase or anti-phase with the exciting signal. The five phase detectors 29 connected to the conductors 10 to 14 apply output signals to five output leads 30 to 34 respectively, each output signal having one or the other of two values, notionally 0 and 1, in dependence upon whether the relevant induced signal is in-phase or in anti-phase with the reference. If the induced signal is in anti-phase then the resulting output signal from the appropriate phase detector 29 has the notional value 0, whereas if the induced signal is in-phase the output signal has the notional value 1.

The values of the signals that appear on the output leads 30 to 34 for any angular position of the shaft 6 are together characteristic according to a cyclically-permuted reflected binary code of the shaft position. The five output values are in combination representative of the shaft position to the extent that they identify within which of thirty-two angular ranges of 11.25 degrees the shaft position lies. Taking the centre of the element 5 as the dataum from which to define the shaft position, the thirty-two angular ranges of 11.25 degrees are centred on the centres of the thirty-two spaces 700 to 731 respectively, and these ranges are accordingly referred to as the ranges R00 to R31. In FIGURE 2 the shaft 6 is shown as positioned centrally within the range R00. The values of the output signals that appear on the leads 30 to 34 when the shaft 6 lies within any of the ranges R00 to R31 are indicated in the following table. In the table the values of the signals are set out in descending order of signficance (so that the values of the output signals on the leads 34, 33, 32, 31 and 30 appear in that order) from left to right.

When the position-encoder is operated to provide a digital representation of shaft position in the serial mode, pulses are applied in succession to the terminals 24, 23, 22, 21 and 20, in that order. In these circumstances the five output pulses that are induced in the conductors 8 and 9 are of one or the other polarity (and accordingly have one or the other of the two values and l) in dependence upon the shaft position. The sequence of output values that are obtained in any one of the ranges R00 to R31 is as given in the above table, reading from left to right. It will be appreciated that the output pulse train appears in the conductor 8 while the shaft position is in one of the even ranges R00, R02 R30, and appears in the conductor 9 when the shaft position is in one of odd ranges R01, R03 R321. The two conductors 8 and 9 may of course be connected in series with one another (and consequently then act as a single conductor passing through all the spaces 700 to 731) so as to obtain the output pulse train at a common point irrespective of whether the shaft position is within an even or odd range.

The two conductors 8 and 9 can of course be replaced by a single conductor, however it is preferred to provide the two separate conductors such as 8 and 9, to allow for the use of the position-encoder as the coarse positionencoder in a fine-coarse position-encoding arrangement such as described in the present applicants U.S. patent application Serial No. 1,615 or in R. E. Wrights US. patent application Serial No. 1,614, both filed January 11, 1960 and assigned to the assignee of the present application. An example of the use of two position-encoders (both as described above with reference to FIGURES 1 to 4) in a fine-coarse arrangement, will now be described with reference to FIGURE 6. Basically, the arrangement of FIGURE 6 is an extension of the arrangement which is described above with reference to FIGURE 5, to provide a representation of the angular position of the shaft 6 within sixteen complete revolutions (as opposed to within only one revolution with the arrangement of FIGURE 5 alone). Those components of the arangement shown in FIGURE 6 that are common to the arrangement of FIGURE 5 have been given the same references as in FIGURE 5.

Referring to FIGURE 6, the position-encoder 27 is arranged as in FIGURE 5 to provide output signals on output leads 30 to 34, that are together characteristic of the particular one of the thirty-two angular ranges R00 to R31 within which the shaft position lies. The position-encoder 27 acts as the fine position-encoder, and a further position-encoder 27', which is of exactly the same construction as the encoder 27, is provided to act as the coarse position-encoder. (The components of the position-encoder 27' that directly correspond to the components 8 to 24 of the encoder 27 have references 8' to 24' respectively in FIGURE 6.)

The exciting signal from the source 28 is applied to the position-encoder 27 through an electronic switch 38. The switch 38 is controlled by the output signal that appears on the load 34, and is arranged to apply the exciting signal to one or the other of the conductors 8' and 9' in dependence upon the value of the output signal 6 on the lead 34.. When the value of this latter output signal is 0 the exciting signal is applied through the switch 30 to the conductor 8, and when the value is l the exciting signal is applied to the conductor 9'.

The signals that are induced in the conductors 10 to 14 are applied from the terminals 20 to 24' to five phase detectors 39 respectively (of which only one is shown). The exciting signal supplied by the source 28 is applied to the phase detectors 39 as a reference against which to determine whether the signal induced in the re spective conductors 10' to 14 are in-phase or in antiphase with the exciting signal. The five phase detectors 39 connected to the conductors 10' to 14 apply output signals to five output leads 40 to 4-4 respectively, each output signal having the value 0 when the relevant induced signal is in anti-phase with the reference, and the value 1 when it is in-phase with the reference.

The shaft (not shown) of the position-encoder 27', the shaft 6' say, is coupled to the shaft 6 through gearing (not shown) that has a step-down ratio of 16:1. Thus for rotation of the shaft 6 through one half-revolution, the shaft 6 rotates through a range of 11.25 degrees. There are thirty-two such ranges of 11.25 degrees, R00 to R'31 say, of the shaft 6, and these correspond to the ranges R00 to R31 respectively of the shaft 6. The initial intercoupling of the shafts 6 and 6 is such that (in ideal circumstances) the shafts 6' rotates from one extreme to the other of one of the even ranges R00, R'02 R'30, for each half revolution of the shaft 6 through the sixteen ranges R00 to R15. Consequently (in ideal circumstances) the shaft 6' rotates from one extreme to the other of one of the odd ranges R'01, R03 R31, for each half revolution of the shaft 6 through the sixteen ranges R16 to R31.

The ideal correspondence between the positions of the two shafts 6 and 6' is not normally obtainable in practice owing to imperfections (such as back-lash) in the gearing between the shafts 6 and 6', or owing to inaccuracies in the encoders 27 and 27' themselves. Such imperfections and inaccuracies do not however affect the accuracy of the representation provided by the present arrangement, as will now be explained. It will be assumed in this explanation, that initially the shaft 6 lies within the range R'00 and that the shaft 6 lies within one of the ranges R00 to R15.

While the shaft 6 lies within any of the ranges R00 to R215 the value of the signal appearing on the lead 34 is 0, and therefore the exciting signal from the source 23 is applied through the switch 38 to the winding 8. In these circumstances the same combination of signals, all anti-phase signals, appear in the conductors 10' to 14' throughout the angular range P of the shaft 6'. In fact this same combination of signals would be obtained for any position of the shaft 6 over a range of 5.625 degrees beyond either extremity of the range R00, that is, half-way into either of the two angular ranges R01 and R31. The reason for this is that the conductor 8 lies in the even numbered spaces 7' (corresponding to the even spaces 7 only, so that these are the only spaces that are excited in the encoder 27' while the exciting signal is applied to the conductor 8.

If now the shaft 6 is rotated so as to pass from the angular range R15 into the angular range R16 there is a change in phase of the signal induced in the conductor 14 of the encoder 27. As a result the value of the signal which is now applied to the switch 38 is l, and the switch 30 therefore applies the exciting signal from the source 28 tothe conductor 9' instead of to the conductor 3'. When the shaft 6 passes from the range R15 into the range R16 the shaft 6 is at least in the region of the transition between the ranges R00 and R'01, but, owing for example to imperfections in the gearing, its passage from the range R'00 into the range Rtli may lead or lag behind the passage of the shaft 6 into the range R16. However, irrespective of the exact position of the shaft 6 in the region of the transition from the range R190 to the range R'01, it is the change in phase of the signal induced in the conductor 14 and the consequent switching of the exciting signal from the conductor 8' to the conductor 9, that effects the required change in the combination of signals appearing on the leads 40 to 44.

After the change in phase of the signal induced in the conductor 14, it is the odd numbered spaces 7 only that are excited in the encoder 27 since the exciting signal is then applied to the conductor 9' only. In these circumstances the same combination of signals appear in the conductors 10' to 14- throughout the angular range R01 of the shaft 6', and in fact, for any position of the shaft 6' over a range of 5.625 degrees beyond either extremity of the range R01. The signals induced in the conductors 11 to 14 in this case are all anti-phase signals, whereas the signal which is induced in the conductor 10' is an in-phase signal.

Thus, before the change in phase of the signal in the conductor 14', the signal induced in the conductor 10' is an anti-phase signal, but directly after the phase change it is an in-phase signal. There is therefore a change in the combination of signals apprearing in the conductors 10 to 14 for movement of the shaft 6 from the range R15 into the range R16, and this change is made irrespective of the actual position of the shaft 6 in the region of the transition between the ranges R'00 and R'01 at that time.

The binary number represented by the signals appearing on the leads 40 to 44 and 30 to 33 while the shaft 6 is in the angular range R15 and the shaft 6 is in the angular range R00, is:

the binary digits being arranged here (and also hereinafter) such that reading from left to right, th values and 1, as the case may be, of the respective signals on the leads 44, 43, 42, 41 and 40, and 33, 32, 31 and 30, are given in that order.

On movement of the shaft 6 from the angular range R15 to the angular range R16, this binary number changes to:

The change from 0 to 1 of the binary digit in the fifth place of this binary number occurs exactly at the time when the shaft 6 moves from the range R15 into the range R16. The fact that the digit in the fifth place of the binary number changes exactly at the time when the shaft 6 moves from the range R15 into the range R16, ensures that the binary number provides an unambiguous indication of the position of the shaft 6 irrespective of any imperfections in the gearing between the shafts 6 and 6', and any inaccuracies in the encoder 27.

The same combination of signals appear in the conductors to 14' for further rotation of the shaft 6 throughout the angular range R16 to R31. If however, the shaft 6 is further rotated to pass from the range R31 into the range R00 there is again a change in the phase of the signal induced in the conductor 14. Hence as the shaft 6 passes from the range R3 1 into the range R00 the exciting signal is switched from the conductor 9, back to the conductor 8'. This results in a change in the combination of signals which appear in the conductors 10' to 14' of the coder 27', the resultant combination of values of the signals appearing on the output leads 40 to 44 and 30 to 33 after this change being:

From the above example it will be appreciated that for any rotation of the shaft 6 (in either direction) directly between the angular ranges R00 and R31, or directly between the angular ranges R and R16, the exciting signal is switched from one to the other of the two conductors 8 and 9'. Concurrently with this change there is a resultant change in the combination of pulses which appear on the leads to 44, so that changes in the five most significant digits of the nine digit number that represents the position of the shaft 6 are directly co-ordinated to changes in position of the shaft 6 itself.

Reference is directed to United States Letters Patent No. 3,099,830 dated July 30, 1963 which is concerned with position-encoders that are of a somewhat similar basic form to the position-encoder that is described above with reference to FIGURES 1 to 4. In this connnection, the construction of position-encoder that is described above with reference to FIGURES 1 to 4 has the advantage that the inertial loading upon the shaft 6 is in general less than that which is experienced in comparable circumstances using any of the constructions of position-encorder that are described in the aforesaid United States Letters Patent.

I claim:

1. An electrical position-encoder comprising, a ferromagnetic core, a series of pairs of ferromagnetic teeth on said core, a first electrical conductor extending through spaces between said teeth, a plurality of second electrical conductors each extending through some of the spaces between said teeth in one direction with respect to said first electrical conductor and through others of the spaces between said teeth in the other direction with respect to said first electrical conductor, each of said spaces being characterized by a unique combination of the directions in which said second conductors extend therethrough with respect to said first electrical conductor, and a ferromagnetic bridging element, means to mount the ferromagnetic bridging element at the free ends of a pair of said teeth to provide a relatively low reluctance magnetic path through that pair of teeth and the element and a relatively high reluctance magnetic path between the element and the core other than through that pair of teeth, said means to mount said element permiting relative movement of the element and the teeth to select the particular pair of teeth bridged by the element, the particular combination of inductive coupling between said first and second electrical conductors that is increased due to the presence of said ferromagnetic bridging element being characteristic of the position of said element relative to said core.

2. An electrical position-encoder comprising, a ferromagnetic core, a series of pairs of ferromagnetic teeth on said core, a first electrical conductor extending through spaces between said teeth so that a current in said conductor will tend to produce, in said pairs of said teeth, magnetic flux in one direction in one tooth of each pair and magnetic flux in the other direction in the other tooth of each pair, a plurality of second electrical conductors each extending through some of the spaces between said teeth in one direction with respect to said first electrical conductor and through others of the spaces between said teeth in the other direction with respect to said first electrical conductor, each of said spaces being characterized by a unique combination of the directions in which said second conductors extend therethrough with respect to said first electrical conductor, and a ferromagnetic element mounted for movement relative to said ferromagnetic core along a path parallel to said ferromagnetic teeth, said element being such as to bridge said pairs of teeth selectively, and when so bridging a selected pair, and when a current is present in said first electrical conductor, substantially the whole of the magnetic flux passing through one tooth of the selected pair passes through the other tooth of the pair, the particular combination of inductive coupling between said first and second electrical conductors that is increased due to said bridging of a selected pair of teeth being characteristic of the posi tion of said ferromagnetic element relative to said core.

3. An electrical position-encoder as claimed in claim 2 wherein each second conductor extends through all of the spaces bet-ween said teeth.

4. An electrical position-encoder as claimed in claim 3 wherein each second conductor extends through the same number of the spaces in each direction with respect to the first conductor.

5. An electrical position-encoder as claimed in claim 4, wherein those spaces through which a second conductor extends in the one direction with respect to said first conductor are in groups of 2 adjacent spaces, It being an integer the value of which is constant for each second conductor.

6. An electrical position-encoder as claimed in claim 2 and including a rotatable shaft on which the ferromagnetic element is mounted, said ferromagnetic core being an annular core coaxial with said shaft.

7. An electrical position-encoder according to claim 6, wherein the pairs of ferromagnetic teeth extend radially inwards from the inner circumference of the core, and the ferromagentic element is carried by the shaft to rotate therewith internally of said teeth.

8. An electrical position-encoder according to claim 7 in combination with means to supply an electric current of cyclically varying magnitude to excite said second conductors in turn.

9. An electrical position-encoder according to claim 2, wherein there are two said first electrical conductors, the two first conductors extending alternately with one another through spaces between consecutive teeth on the core, whereby the combination of inductive couplings between the first and second conductors in any space is characteristic of the space and thus of the position of the ferromagnetic element relative to said core.

10. An electrical position-encoder according to claim 9 wherein the ferromagnetic element extends a distance of approximately twice the tooth-pitch along the path.

11. An electrical position-encoding arrangement including a position-encoder according to claim 10, said position-encoder distinguishing between each of a plurality of ranges of position of the ferromagnetic element, and means to supply electric current of cyclically varying magnitude to excite a selected one of the first conductors in dependence upon which of two sets of alternate ones of said plurality of ranges of position is occupied by said ferromagnetic element.

12. An electrical position-encoding arrangement according to claim 11, including a second position-encoder comprising a ferromagnetic core, a series of pairs of ferromagnetic teeth on said core, a first electrical conductor extending through spaces between said teeth so that a current in said conductor will tend to produce, in said pairs of said teeth, magnetic flux in one direction in one tooth of each pair and magnetic flux in the other direction in the other tooth of each pair, a plurality of second electrical conductors each extendin through some of the spaces between said teeth in one direction with respect to said first electrical conductor and through others of the spaces between said teeth in the other direction with respect to said first electrical conductor, each of s d spaces being characterized by a unique combination of the directions in which said second conductors extend therethrough with respect to said first electrical conductor, and a ferromagnetic element mounted for movement relative to said ferromagnetic core along a path parallel to said ferromagnetic teeth, said element being such as to bridge said pairs of teeth selectively, and when so bridging a selected pair, and a current is present in said first electrical conductor, substantially the whole of the magnetic flux passing through one tooth of the selected pair passes through the other tooth of the pair, the particular combination of inductive coupling between said first and second electrical conductors that is increased due to said bridging of a selected pair of teeth being characteristic of the position of said ferromagnetic element relative to said core, the first-mentioned and said second position-encoders being coupled by gearing to provide coarse and fine representations respectively of said ferromagnetic element position, the position-encoding arrangement also including selecting means to effect the selection of said one of said first conductors, said selecting means being responsive to a change from one to a next of said plurality of ranges of position as indicated by said fine representation.

13. An electrical position-encoder according to claim 2 in combination with means to supply electric current of cyclically varying magnitude to excite the second conductors in turn.

References Cited by the Examiner UNITED STATES PATENTS 2,930,033 3/1960 Webb 340-347 2,931,023 3/1960 Quade 340-347 3,066,286 11/1962 Wright 340347 MALCOLM A. MORRISON, Primary Examiner. 

1. AN ELECTRICAL POSITION-ENCODER COMPRISING, A FERROMAGNETIC CORE, A SERIES OF PAIRS OF FERROMAGNETIC TEETH ON SAID CORE, A FIRST ELECTRICAL CONDUCTOR EXTENDING THROUGH SPACES BETWEEN SAID TEETH, A PLURALITY OF SECOND ELECTRICAL CONDUCTORS EACH EXTENDING THROUGH SOME OF THE SPACES BETWEEN SAID TEETH IN ONE DIRECTION WITH RESPECT TO SAID FIRST ELECTRICAL CONDUCTOR AND THROUGH OTHERS OF THE SPACES BETWEEN SAID TEETH IN THE OTHER DIRECTION WITH RESPECT TO SAID FIRST ELECTRICAL CONDUCTOR, EACH OF SAID SPACES BEING CHARACTERIZED BY A UNIQUE COMBINATION OF THE DIRECTIONS IN WHICH SAID SECOND CONDUCTORS EXTEND THERETHROUGH WITH RESPECT TO SAID FIRST ELECTRICAL CONDUCTOR, AND A FERROMAGNETIC BRIDGING ELEMENT, MEANS TO MOUNT THE FERROMAGNETIC BRIDGING ELEMENT AT THE FREE ENDS OF A PAIR OF SAID TEETH TO PROVIDE A RELATIVELY LOW RELUCTANCE MAGNETIC PATH THROUGH THAT PAIR OF TEETH AND THE ELEMENT AND A RELATIVE HIGH RELUCTANCE MAGNETIC PATH BETWEEN THE ELEMENT AND THE CORE OTHER THAN THROUGH THAT PAIR OF TEETH, SAID MEANS TO MOUNT SAID ELEMENT PERMITING RELATIVE MOVEMENT OF THE ELEMENT AND THE TEETH TO SELECT THE PARTICULAR PAIR OF TEETH BRIDGED BY THE ELEMENT, THE PARTICULAR COMBINATION OF INDUCTIVE COUPLING BETWEEN SAID FIRST AND SECOND ELECTRICAL CONDUCTORS THAT IS INCREASED DUE TO THE PRESENCE OF SAID FERROMAGNETIC BRIDGING ELEMENT BEING CHARACTERISTIC OF THE POSITION OF SAID ELEMENT RELATIVE TO SAID CORE. 